Brazed ceramic-metal composite

Abstract

A composite consists of a ceramic brazed to another ceramic by means of a joint layer therebetween. The joint layer comprises a porous metal interlayer and an active brazing filler metal penetrating through the porous metal interlayer.

I claim: 
     
       1. A composite consisting of an alumina brazed to alumina by means of a joint layer therebetween, the joint layer comprising a porous metal interlayer and an active brazing filler metal penetrating through the porous metal interlayer, said composite having been brazed at a temperature lower than the melting point of the porous metal interlayer so that melting of the porous metal interlayer does not occur during brazing, the porous metal interlayer not substantially alloying with the active brazing filler metal during brazing, the porous metal interlayer being tungsten. 
     
     
       2. The composite of claim 1 wherein the active brazing filler metal is a Cu-Si-Ti-Al alloy having a coefficient of expansion of 16.5×10 -6  /°C. and wherein the volume ratio of filler metal to tungsten in the joint layer of filler metal and tungsten is about 30 to 70 so that the coefficient of expansion of said joint layer is about 8×10 -6  /°C. 
     
     
       3. A composite consisting of a ceramic brazed to a ceramic by means of a joint layer therebetween, the joint layer comprising a porous metal interlayer and an active brazing filler metal penetrating through the porous metal interlayer, said composite having been brazed at a temperature lower than the melting point of the porous metal interlayer so that melting of the porous metal interlayer does not occur during brazing, the porous metal interlayer not substantially alloying with the active brazing filler metal during brazing, the coefficient of expansion of the metal comprising the porous metal interlayer being lower than the coefficient of expansion of the ceramics, the coefficient of expansion of the brazing filler metal being higher than the coefficient of expansion of the ceramics, the volume ratio of the porous interlayer metal and the brazing filler metal being such that the coefficient of expansion of the joint layer approximates the coefficient of expansion of the ceramics. 
     
     
       4. The composite of claim 3 where the ceramics are the same. 
     
     
       5. The composite of claim 3 where the porous interlayer metal is tungsten. 
     
     
       6. The composite of claim 3 where the ceramics are alumina.